1. Field of the Invention
The present inventions relate to pollution reducing devices and methods. In particular, the present invention relates to the field of methods and devices for trapping particulate matter suspended in exhaust from, for example, an automotive diesel engine.
2. Description of the Related Art
Diesel engines provide very efficient power from a given amount of fuel, and they are able to use significantly less expensive fuels than gasoline engines. Thus, for trucks, buses, railroad locomotives, generators, and even automobiles, the diesel engine is preferred over the gasoline engine. The major drawback to diesel powered vehicles is the exhaust pollution, which is quite different than generated from a gasoline engine. The diesel engine has fuel injected into the cylinder at a point when air in the cylinder has reached a high degree of compression.
Highly compressed air reaches temperatures above the ignition point of diesel fuel, so the fuel sprayed via injector into the cylinder spontaneously ignites at the temperature of the compressed air and, by dint of the hot burning gases generated, the piston is impelled down the cylinder and power is provided to gear, wheel, and propeller. The problem is that the temperature is not uniform throughout the cylinder and some small portions of the fuel will not burn but rather be subject to reduction (carbon-hydrogen bond broken and carbon-carbon bond formed) as well as combustion (carbon-hydrogen bond broken and carbon-oxygen and hydrogen-oxygen bonds formed).
The exhaust eventually expelled from the cylinder (as a four-stroke engine), the next compression stroke will push gases out of the cylinder and into the manifold which first receives the exhaust. The exhaust gases (mostly oxides of carbon, hydrogen, and nitrogen) carry these small particles (called particulates) with them. If these particulates leave the tailpipe of the car or the stack of the truck, boat, train, or bus, they are released into the air around the road, waterway, street, and railroad. In cities, a fine black dust settles over the area (very common in some cities) and the air itself carries the particulate to people who breathe this dust. It is not only filthy, but it has also been shown in some studies to cause cancer and to aggravate some conditions, such as asthma.
Government environmental regulations have focused on the need to remove particulates from diesel exhaust and thus the environment. Three approaches have been used: (1) modify the fuel to engender more complete combustion, (2) modify the engine to make combustion more complete, and (3) modify the exhaust system to remove, trap, and/or (once the particulates have left the cylinder where they originated) further subject them to high temperature and/or catalytic combustion. The options above (1) and (2) are expensive; (1) will affect all diesel engines for which the modified fuel is used and (2) will affect only the new engines which incorporate this technology. What are needed, therefore are novel solutions that address option (3) above; that is, to focus on the exhaust system for the solution to the particulate pollution problem.